Traditional motor structures, such as those driven by direct current (“DC”) currents, are classified as either brushed or brushless motors. These two types of motor structures implement different commutation techniques and structures. Commutation refers to the action of selectably delivering power (e.g., described in terms of currents or voltages) to energize coils at proper motor phases to produce torque. Brushless motors operate by electronically commutating phase currents passing through stationary windings of a stator to magnetically interact with permanent magnets on a rotor. In brushless motors, an external electronic driver switches the application of currents to the stator windings. These currents then produce magnetic fields to generate torque on the permanent magnets. Brushed motors, however, use electromechanical components, or “brushes,” to commutate the DC current in a winding (i.e., armature coil) on a rotor. The permanent magnets of a brushed DC motor remain stationary. The windings of the brushed motors are connected to different segments of a field pole commutator to make contact with brushes carrying the positive and negative voltages of the power supply. As the rotor rotates, different segments of the commutator come in contact with the brushes such that the coils are powered in a sequence, thereby perpetuating rotation of a shaft. FIGS. 1 and 2 depict the structural differences between brushless and brushed motors.
FIG. 1 illustrates a structure for a traditional brushless direct current (“DC”) electric motor. Brushless DC electric motor 100 includes a first plate 108, a yoke 106 composed of laminations, a rotor assembly 104, and a second plate 102. Laminated yoke 106 supports coils (not shown) and also provides a mounting surface for joining first plate 108 with second plate 102. At least one drawback to brushless DC electric motor 100 is that laminated yoke 106 generally forms suboptimal flux paths. Another drawback is that the external electronic driver (i.e., controller) that controls commutation for brushless DC electric motor 100 is relatively more complicated and thus more expensive to implement than a commutator and a set of brushes used in brushed DC electric motors.
FIG. 2 illustrates a structure for a traditional brushed direct current (“DC”) electric motor. Brushed DC electric motor 200 includes an end plate 202, a rotor assembly 204, and a housing 206. End plate 202 includes brushes 201 to make and break contact with commutation segments on commutator 203, thereby commutating power to a rotor assembly 204. It is rotor assembly 204 that includes one or more coils 207 in slots. Housing 206 is deep-drawn (i.e., it has been formed to have a deep housing cavity) and is configured to capture a first bearing (not shown) and one end of a shaft 205. Note that housing 206 can provide datum surfaces to locate and align end plate 202. End plate 202 is configured to capture a second bearing (not shown) and the other end of shaft 205. At least one drawback is that thermal energy, or heat, is generated by the one or more coils at a location that is relatively distant from the outside surface of the motor, thereby making it relatively difficult for heat to dissipate from the coils of rotor assembly 204. As such, the thermal resistance of brushless DC electric motor 100 is lower than that of brushed DC motor 200.
FIGS. 3A to 3D illustrate various aspects of traditional brushed DC electric motor 200 of FIG. 2. FIG. 3A shows a rotor assembly 300 for brushed DC electric motor 200 in which windings 207 are wound in slots (FIG. 2). Also shown is a commutator 203 and shaft 205. FIG. 3B illustrates stationary permanent magnets 304 being mounted to an inner diameter of housing 206. FIG. 3C depicts rotor assembly 300 of FIG. 3A residing in housing 206 of FIG. 3B. FIG. 3D shows brushes 306 contacting commutator 203. Brushes 306 can be of a different kind than brushes 201 of FIG. 2.
In view of the foregoing, it would be desirable to provide improved commutation techniques and structures that minimize at least one of the drawbacks in each of the conventional direct current (DC) electric motors.